1. Field of the Invention
The present invention relates a gas nozzle device used in a gaseous polishing apparatus to produce a flat surface by removing surface irregularities on an object such as a semiconductor wafer using a reactive polishing gas to polish/etch, or conversely, to fabricate surface structures on the surface by means of gaseous etching.
2. Description of the Related Art
A method of producing a flat surface on a substrate wafer is known as chemical mechanical polishing (CMP) in which a surface to be polished of a wafer which is held in a wafer holding device is pressed and rotated against an abrading surface of a polishing table while supplying a polishing solution, suitable for the material being polished, at the abrading interface.
However, the CMP process is designed to produce flatness by polishing the entire surface of a wafer, and therefore, it is not suitable for removing local surface irregularities, such as those shown in FIG. 1, and it often requires unnecessary removal of much surface material and suffers from low productivity.
For this reason, another known approach to obtaining a flat surface is to arrange a gas eject nozzle opposite to an object to be polished, such as semiconductor wafer, and eject a reactive gas onto the surface to remove macroscopic surface irregularities by gaseous etching.
A method of gaseous polishing shown in FIG. 2 is generally known, in which an object 101 to be polished is placed on a susceptor 102 in a polishing chamber 103. The chamber 103 is then evacuated through an exhaust port 104 to a reduced pressure, and a polishing gas is introduced into the polishing chamber 103, under reduced pressure, and the polishing gas is directed to a desired spot to be polished, from the nozzle opening of a polishing gas inlet tube (nozzle) 105 towards the object 101, for a given duration of time.
A typical chemical reaction which takes place for silicon is shown in equation (1) below. The polishing gas (F*, * indicating an active state of fluorine gas) ejected from the tip of the nozzle 105 impacts the surface of the object 101, a silicon wafer in this case, and forms a reaction product SiF4 which vaporizes and removes surface material from the object 101.
Si+4F*xe2x86x92SiF4↑+C2F6 xe2x80x83xe2x80x83(1)
Excess polishing gas is exhausted from the polishing chamber 103, as indicated by arrows in FIG. 2, through the exhaust port 104.
As discussed above, although the unreacted polishing gas is removed form the polishing chamber 103 through the exhaust port 104, when the distance to the exhaust port 104 is long, etching can occur on locations other than a targeted location, resulting in removal of surface material from areas other than the desired location. This extraneous etching action causes serious problems in surface flatness. This effect may not be so serious when the material to be removed ranges in thickness from several micrometers to several tens of micrometers, but it can cause serious damage to the quality of a polished surface when it is necessary to perform precision polishing, in other words, removal of surface material of the order of several hundred angstroms to several thousands angstroms.
It is an object of the present invention to provide a gaseous polishing apparatus and a nozzle device designed for gaseous polishing so as to perform precision polishing only on a local target area on a surface of an object to be polished.
Such object is achieved in a nozzle device, to be disposed close to a local target area of a surface to be polished, for gaseous polishing of such surface of an object placed inside a polishing chamber. The nozzle device directs a polishing gas to the local target area from a nozzle opening provided at a downstream end of an eject nozzle of the nozzle device. A shutter device is disposed in proximity to the nozzle opening so as to control protecting or exposing the surface to the polishing gas. A control mechanism controls opening and closing operation of the shutter device.
Accordingly, a space between the shutter device and an open end of the nozzle is made small so as to decrease a lag in response between the opening/closing operations of the shutter device and start/stop actions of flowing the gas, thus to improve polishing precision. That is, only a desired amount of material is removed from a targeted area.
It is preferable that the shutter device and the control mechanism include a shield member freely movably supported in a vicinity of the nozzle opening of the eject nozzle. A moving device places the shield member either in a shielding position to block a gas stream ejected from the eject nozzle or in an exposing position to enable a local area of the surface to be exposed to the polishing gas.
It is preferable that the shutter device comprises valve means disposed in a vicinity of the nozzle opening in a gas flow passage within the eject nozzle for blocking or ejecting the polishing gas. A control device remotely controls opening and closing operations of the valve means.
It is also preferable that the shutter device and the control mechanism include a shield member disposed so as to shield areas other than the targeted location from the polishing gas ejected from the eject nozzle, and an attaching device for attaching the shield member to an outer periphery of the eject nozzle so as to be freely vertically movable.
Therefore, after finishing polishing of a local area, the shield plate is positioned in front of the nozzle opening before the nozzle is moved to a next target location. By so doing, unintended etching of areas other than the targeted area by the polishing gas can be prevented while the nozzle is being relocated. Also, by shutting the nozzle opening using the shutoff valve after a given amount of polishing has been completed, areas other than targeted areas are prevented from being etched, thereby enabling precision of the polishing operation.
It is preferable that gaseous polishing be followed by a chemical mechanical polishing process, so that gaseous polishing is used first to etch off relatively macroscopic surface irregularities, followed by the CMP process to polish fine surface irregularities, thereby providing precision polishing at high efficiency.
It is another object of the present invention to provide a polishing apparatus to replace or to be used in association with a conventional mechanical and chemical polishing apparatus to produce a high quality flat surface in a more efficient manner.
Gaseous polishing of a local area of a workpiece is achieved by ejecting a reactive polishing gas as pulsed ejections from a gas eject nozzle towards a target location at a high speed. A high speed in this context means that the velocity of the polishing gas ejected from the nozzle is in a range of sonic to ⅕ sonic speed, which has never been utilized in conventional gaseous polishing. The surface may be exposed to the polishing gas under a reduced pressure. The depth of etched profile may be controlled by adjusting the frequency of pulsed ejections.
A gaseous polishing apparatus for polishing a local area by exposure to pulsed ejections of the polishing gas ejected from the gas eject nozzle at a high speed comprises: the gas eject nozzle for ejecting the polishing gas, a gas supply device to supply the polishing gas to the gas eject nozzle, and a gas eject control device to produce high-speed pulsed ejections of the polishing gas.
The gas eject nozzle and the workpiece may be placed inside a vacuum chamber. The gas supply device may be provided with a gas reservoir for storing the polishing gas at a specific pressure in an upstream location of the gas eject nozzle. The gas reservoir is controlled by the gas eject control device so as to eject the polishing gas from the gas reservoir as pulsed ejections.
The gas eject control device may include a shutter device comprised by either a rotating disc or an electromagnetic valve, for controlling closing or opening of a gas opening of the gas eject nozzle, so that pulsed ejections are produced by controlling opening or closing of the shutter device. The gas eject control device may include a parameter selection device for controlling pulse duration and pulse frequency so as to adjust an amount of material to be polished.
A polishing facility may be comprised by combining the gaseous polishing apparatus described above with a CMP apparatus to provide additional chemical and/or mechanical polishing to a gas polished surface.
Another embodiment of the present invention is a nozzle device for ejecting a reactive polishing gas to a specific location on an oppositely disposed surface of a workpiece so as to polish surface structures on the surface, wherein a nozzle has a gas passage space provided at an upstream end and a gas hole or opening formed on a downstream side of the nozzle.
Accordingly, it is possible to minimize flow resistance through the nozzle, so that response to control can be improved to provide a polishing apparatus that is superior in controlling the etched profile.
The nozzle may include a tube member to extend towards the surface to be polished and a shutter disc member to close a downstream end of the tube member, the gas hole or opening being formed on the shutter disc member. Accordingly, a relatively simple structure can be used to lower flow resistance through a fine gas hole. Thickness t of the shutter disc member may be selected in a range of 10 to 1,000 xcexcm. By so doing, flow resistance can be controlled using a practical material while maintaining a certain degree of strength.
A plurality of nozzles may be provided. Such a nozzle assembly can polish a larger area effectively. The nozzle may be comprised by a tube member to extend towards the surface and a header section disposed at a downstream end of the tube member. Such a design allows a larger area to be polished more uniformly.